Just to be clear, there is no such thing as a "management network" or a "management interface" on an Isilon cluster. Isilon is managed in-band, and as-such any IP interface that's in the system access zone can access the WebUI, SSH, make PlatformAPI calls over HTTPS, etc. This doesn't work in non-system access zones, but that's more of a the feature isn't there yet, but could be in the future. It would in some instances make sense to allow for instance; in a multi-tenant environment, each tenant to be able to login to the WebUI, and see only their settings, shares, exports, etc. The same goes for the Platform API or the CLI over SSH. So while, for now you can make the assumption that anything not in the system access zone isn't a "management network", that could only be a temporary condition. There is no IPMI/ ILO/ Control Station/ DRAC for managing Isilon out-of-band.
I wrote some more on this subject in this doc if you're up for a read:
(See page 9, specifically)
Principal SE, Datadobi